SARS-CoV-2 spike-specific regulatory T cells (Treg) expand and develop memory in vaccine recipients suggesting a role for immune regulation in preventing severe symptoms in COVID-19
https://www.tandfonline.com/doi/full/10.1080/08916934.2023.2259133

Abstract
We enrolled healthy subjects that received 2 to 4 injections of mRNA-based vaccination to prevent COVID-19 months to a year from the last vaccine boost, and we found numerous SARS-CoV-2 spike-specific regulatory T cell (Treg) that developed T cell memory as effector memory T cells (TEM) and central memory T cells (TCM). CD4+ CD25high Treg expressed the chemokine receptor CCR6 in a considerable percentage, suggesting T cell homing to the vascular endothelium, lung and gut epithelial cells and brain.